Host resistance elicited by methyl jasmonate reduces emission of aggregation pheromones by the spruce bark beetle, Ips typographus

We treated Norway spruce (Picea abies) stems with methyl jasmonate (MeJA) to determine possible quantitative and qualitative effects of induced tree defenses on pheromone emission by the spruce bark beetle Ips typographus. We measured the amounts of 2-methyl-3-buten-2-ol and (S)-cis-verbenol, the two main components of the beetle's aggregation pheromone, released from beetle entrance holes, along with phloem terpene content and beetle performance in MeJA-treated and untreated Norway spruce logs. As expected, phloem terpene levels were higher and beetle tunnel length was shorter (an indication of poor performance) in MeJA-treated logs relative to untreated logs. Parallel to the higher phloem terpene content and poorer beetle performance, beetles in MeJA-treated logs released significantly less 2-methyl-3-buten-2-ol and (S)-cis-verbenol, and the ratio between the two pheromone components was significantly altered. These results suggest that host resistance elicited by MeJA application reduces pheromone emission by I. typographus and alters the critical ratio between the two main pheromone components needed to elicit aggregation. The results also provide a mechanistic explanation for the reduced performance and attractivity observed in earlier studies when bark beetles colonize trees with elicited host defenses, and extend our understanding of the ecological functions of conifer resistance against bark beetles.     

The bark beetle Pityogenes chalcographus (L.) (Scolytidae) in living trees: reproductive success, tree mortality and interaction with Ips typographus

Abstract:  Tree-killing ability of Pityogenes chalcographus was experimentally investigated by baiting living spruce Picea abies with synthetic aggregation pheromone, thereby exposing them to beetle attack. Reproductive success was estimated by rearing beetles from stem sections taken from killed trees. The presence of Ips typographus on several killed trees allowed a comparison of reproductive success in the presence and absence of this species. Furthermore, the possibility that breeding material colonized by P. chalcographus may induce subsequent attacks by I. typographus on nearby trees was also studied. The tree killing ability of P. chalcographus was low as only 8% of the baited trees, attacked by P. chalcographus alone, were killed. Tree death was strongly related to the presence of I. typographus , which is in line with the association with aggressive wood-living fungi in this species. The reproductive success was low, with on average less than one daughter beetle produced per mother beetle. The success was significantly higher in trees also inhabited by I. typographus . Tree-parts colonized by P. chalcographus induced almost no attacks by I. typographus on nearby trees.     

The role of semiochemicals in tritrophic interactions between the spruce bark beetle Ips typographus, its predators and infested spruce

Abstract:  Semiochemical interactions between the spruce bark beetle Ips typographus , its predators Medetera setiventris , Thanasimus formicarius and Thanasimus femoralis , and the host Norway spruce, Picea abies , were studied in the field. The chemicals S - cis -verbenol, 2-methyl-3-buten-2-ol, ipsdienol, (+)- α -pinene, (−)- α -pinene, (±)- α -pinene, limonene, camphor and their naturally occuring mixtures were used as trap baits in a multiple-choice design that allowed for comparison of their attractivity for the focal species. Medetera was attracted to both the prey aggregation pheromone and its multifunctional component, ipsdienol. On the contrary, both Thanasimus species responded predominantly to ipsdienol and less to the prey aggregation pheromone. In the case of I. typographus , the attractivity of aggregation pheromone seems to be increased by the addition of a mixture of monoterpenic tree volatiles, and by addition of ipsdienol. Bark beetles and predators showed species-specific responses to volatile mixtures representing different stages of tree decay and different stages of bark beetle colony establishment. These responses correlates with the optimal foraging habitat of each species. None of the predator species responded to 2-methyl-3-buten-2-ol, a substantial component of I. typographus pheromonal bouquet, thus it is hypothesized that only substances of monoterpenic origin attract predators.     

Priming of inducible defenses protects Norway spruce against tree-killing bark beetles

Plants can form an immunological memory known as defense priming, whereby exposure to a priming stimulus enables quicker or stronger response to subsequent attack by pests and pathogens. Such priming of inducible defenses provides increased protection and reduces allocation costs of defense. Defense priming has been widely studied for short-lived model plants such as Arabidopsis, but little is known about this phenomenon in long-lived plants like spruce. We compared the effects of pretreatment with sublethal fungal inoculations or application of the phytohormone methyl jasmonate (MeJA) on the resistance of 48-year-old Norway spruce (Picea abies) trees to mass attack by a tree-killing bark beetle beginning 35 days later. Bark beetles heavily infested and killed untreated trees but largely avoided fungus-inoculated trees and MeJA-treated trees. Quantification of defensive terpenes at the time of bark beetle attack showed fungal inoculation induced 91-fold higher terpene concentrations compared with untreated trees, whereas application of MeJA did not significantly increase terpenes. These results indicate that resistance in fungus-inoculated trees is a result of direct induction of defenses, whereas resistance in MeJA-treated trees is due to defense priming. This work extends our knowledge of defense priming from model plants to an ecologically important tree species.     

Exogenous application of methyl jasmonate elicits defenses in Norway spruce (Picea abies) and reduces host colonization by the bark beetle Ips typographus

The terpenoid and phenolic constituents of conifers have been implicated in protecting trees from infestation by bark beetles and phytopathogenic fungi, but it has been difficult to prove these defensive roles under natural conditions. We used methyl jasmonate, a well-known inducer of plant defense responses, to manipulate the biochemistry and anatomy of mature Picea abies (Norway spruce) trees and to test their resistance to attack by Ips typographus (the spruce bark beetle). Bark sections of P. abies treated with methyl jasmonate had significantly less I. typographus colonization than bark sections in the controls and exhibited shorter parental galleries and fewer eggs had been deposited. The numbers of beetles that emerged and mean dry weight per beetle were also significantly lower in methyl jasmonate-treated bark. In addition, fewer beetles were attracted to conspecifics tunneling in methyl jasmonate-treated bark. Stem sections of P. abies treated with methyl jasmonate had an increased number of traumatic resin ducts and a higher concentration of terpenes than untreated sections, whereas the concentration of soluble phenolics did not differ between treatments. The increased amount of terpenoid resin present in methyl jasmonate-treated bark could be directly responsible for the observed decrease in I. typographus colonization and reproduction.     

Characteristics of Norway spruce trees (Picea abies) surviving a spruce bark beetle (Ips typographus L.) outbreak

The characteristics of spruce individuals, which survived a massive bark beetle outbreak, were compared with the characteristics of neighbouring attacked trees in Šumava National Park (Czech Republic). Selected parameters related to crown geometry, stand conditions and distances between trees were measured or estimated. Significant differences were found between the surviving trees and the neighbouring trees attacked by I. typographus. Trees with a higher level of stem shading (longer crown length) tended to survive. The attacked trees were usually located in areas with larger basal area, especially southwards from them. A shorter distance to a previously attacked tree increased the probability of additional attack. Spruce trees with more progressive crown structure transformation (primary structure defoliation) were significantly more frequently attacked by spruce bark beetle. Superior and taller trees had a clearly longer life expectancy than dominant ones. These results show that the attack of trees by bark beetle can be predicted to a certain degree, which can be used in management of endangered spruce forests.     

Behavior of male and female spruce bark beetles,Ips typographus,on the bark of host trees during mass attack

The behavior of 118 spruce bark beetles, Ips typographus,was observed on trees under colonization. Most individuals were followed from when they landed until they entered or left the tree. Both males and females spent most time inspecting crevices and searching for a place to start boring or for a hole to enter. These behaviors accounted for 87 and 70% of all behavioral acts recorded for males and females, respectively. Females entered galleries with males only after a period of pushing at the gallery entrance. Males spent on average 3 min and females 4 min on the bark before entering or leaving the tree. Thirty-three percent of the beetles eventually entered the tree, 31% flew away, 35% dropped from the host, and one beetle was eaten by a predator. The results are discussed in relation to the question of mate choice in bark beetles and to studies on attack dynamics of spruce bark beetle populations.     

The Red-belted Bracket (Fomitopsis pinicola) colonizes spruce trees early after bark beetle attack and persists

The Red-belted Bracket (Fomitopsis pinicola) is one of the major decomposers of coniferous wood in Europe and can reach high densities after outbreaks of bark beetles. However, factors of dead wood type and decay stage, which determine the growth of reproductive biomass, i.e. basidiomes, remain unclear. In 2013, we surveyed 1280 dead wood objects and vital trees in spruce stands killed by the bark beetle Ips typographus in 2012, 2002, 1992 and in undisturbed stands for the presence, number, mean basidiome size and total volume of basidiomes. Living basidiomes were equally abundant on dead wood 1, 11, and 21 y after bark beetle outbreak, but were lacking on living trees. Our results indicate that F. pinicola is an effective early colonizer of the huge resource pulse of dead wood caused by the outbreak of bark beetles and basidiomes can persist for 21 y.     

Fungal associates of the tree-killing bark beetle,Ips typographus,vary in virulence,ability to degrade conifer phenolics and influence bark beetle tunneling behavior

The bark beetle Ips typographus carries numerous fungi that could be assisting the beetle in colonizing live Norway spruce (Picea abies) trees. Phenolic defenses in spruce phloem are degraded by the beetle's major tree-killing fungus Endoconidiophora polonica, but it is unknown if other beetle associates can also catabolize these compounds. We compared the ability of five fungi commonly associated with I. typographus to degrade phenolic compounds in Norway spruce phloem. Grosmannia penicillata and Grosmannia europhioides were able to degrade stilbenes and flavonoids faster than E. polonica and grow on minimal growth medium with spruce bark constituents as the only nutrients. Furthermore, beetles avoided medium amended with phenolics but marginally preferred medium colonized by fungi. Taken together our results show that different bark beetle-associated fungi have complementary roles in degrading host metabolites and thus might improve this insect's persistence in well defended host tissues.     

Spatio-temporal impact of climate change on the activity and voltinism of the spruce bark beetle, Ips typographus

The spruce bark beetle Ips typographus is one of the major insect pests of mature Norway spruce forests. In this study, a model describing the temperature-dependent thresholds for swarming activity and temperature requirement for development from egg to adult was driven by transient regional climate scenario data for Sweden, covering the period of 1961–2100 for three future climate change scenarios (SRES A2, A1B and B2). During the 20th century, the weather supported the production of one bark beetle generation per year, except in the north-western mountainous parts of Sweden where the climate conditions were too harsh. A warmer climate may sustain a viable population also in the mountainous part; however, the distributional range of I. typographus may be restricted by the migration speed of Norway spruce. Modelling suggests that an earlier timing of spring swarming and fulfilled development of the first generation will significantly increase the frequency of summer swarming. Model calculations suggest that the spruce bark beetle will be able to initiate a second generation in South Sweden during 50% of the years around the mid century. By the end of the century, when temperatures during the bark beetle activity period are projected to have increased by 2.4–3.8 °C, a second generation will be initiated in South Sweden in 63–81% of the years. The corresponding figures are 16–33% for Mid Sweden, and 1–6% for North Sweden. During the next decades, one to two generations per year are predicted in response to temperature, and the northern distribution limit for the second generation will vary. Our study addresses questions applicable to sustainable forest management, suggesting that adequate countermeasures require monitoring of regional differences in timing of swarming and development of I. typographus , and planning of control operations during summer periods with large populations of bark beetles.     

Pre-treatment with salicylic acid induces phenolic responses of Norway spruce (<Emphasis Type="Italic">Picea abies</Emphasis>) bark to bark beetle (<Emphasis Type="Italic">Ips typographus</Emphasis>) attack

Keymessage

The temporal gradations of the investigated phenolics in Norway spruce bark after bark beetle (Ips typographus) attack followed the general eco-physiological concept. Treatment with salicylic acid inhibits bark beetle colonisation, alleviates the phenolic responses and activates the synthesis of condensed tannins on later sampling dates.

Abstract

Conifer bark is the target of numerous organisms due to its assimilated transport and nutrient storage functions. In the presented study, 100 mM salicylic acid (SA) was applied onto Norway spruce stems prior to being infested with bark beetles (Ips typographus L.), to study the temporal gradation of changes in condensed tannins (CT) and total phenolics (tPH) and their significance for mediating stress-tolerance. A significant accumulation of CT was monitored in untreated trees in response to progressive bark beetle infestation occurring from May onwards. In SA-treated infested trees, the CT values remained at control levels until May, but after the re-treatment of infested trees in June, the concentrations of CT rose significantly in comparison to the controls. The tPH values dropped 16 days after SA-treatment, independent of infestation, and later on remained at control level until July. In contrast, tPH contents accumulated in untreated infested trees in May, eased in June and increased again in July, when the trees were affected by the second generation of bark beetles. To sum up, in May and July when the highest beetle-flight activity was monitored the metabolic shift of phenolics within untreated infested trees differed significantly from the response of SA-treated trees. In addition, on SA-treated trees less entrance holes were monitored over the whole period of sampling when compared to untreated infested trees. These results provide evidence that SA-treatment alleviates the phenolic responses, activates the synthesis of condensed tannins and inhibits bark beetle colonisation.

     

Past attacks influence host selection by the solitary bark beetle Dendroctonus micans

1. A spatio‐temporal study of host selection and local spread of a solitary bark beetle attacking live spruce Dendroctonus micans (Kugelann) was carried out using a combination of standard statistical methods, geostatistical analyses, and modelling. The study was based on data from three plots (150–300 trees, 0.3–1 ha) from 1978 to 1993. All trees were mapped and successful and abortive bark‐beetle attacks on each tree were counted annually. Because the attacked trees usually survived, temporal attack patterns as well as spatial patterns could be analysed. 2. The distribution of successful insect attacks on the trees was slightly aggregative, indicating some degree of choice rather than totally random establishment. 3. The level of yearly individual attacks per tree was very stable, suggesting that D. micans usually leave the host in which they develop. 4. The attacked trees were distributed randomly in the plots; at the study's spatial scale, the insects dispersed freely throughout the plot (no spatial dependence). 5. On the other hand, time dependence was strong; some trees were attacked repeatedly while others were left untouched. 6. Among a choice of scenarios (random attack, fixed variability in individual host susceptibility, induced host susceptibility following random attack), the best fit was obtained with the model involving induced individual host susceptibility. This type of relation to the host tree contrasts strongly with patterns generally described in host–plant relationships (including gregarious, tree‐killing bark beetles), where local herbivore damage results in induced resistance. 7. These results suggest that the first attacks in a new stand are made at random, that all or most of the beetles emerging from a tree disperse and resample the stand, and that they settle preferentially on trees that were colonised successfully by previous generations.     

Specialization of the olfactory receptor cells in the bark beetleIps typographus and its predatorThanasimus formicarius to bark beetle pheromones and host tree volatiles

Summary Olfactory receptor cells of the spruce bark beetle,Ips typographus, and its predator, the clerid beetleThanasimus formicarius, were studied using electrophysiological techniques. Recordings were made of nerve impulses from single cells and of the summated receptor potential (electroantennogram).Information from bark beetle pheromones and host volatiles is detected by separate olfactory receptor cells inI. typographus. Those which detected bark beetle pheromones responded to only one key substance. Some receptor cells which responded to spruce bark volatiles were strongly activated by one of the synthetic host compounds tested. However, too few host compounds were tested to reach definite conclusions about the specialization of host odour cells. T. formicarius has evolved olfactory receptor cells for bark beetle pheromones. These have similar specificities (specialist types) to those of the bark beetles. Furthermore, the predator has olfactory receptor cells for many bark beetle pheromones. This indicates thatT. formicarius is able to detect and discriminate between many bark beetle species. No significant differences were found between prey and predator cells which responded to host volatiles.     

Can Norway spruce trees be ‘vaccinated’ against attack by Ips typographus?

1 A field experiment was carried out to test the hypothesis that treatment of Norway spruce trees with the Ips typographus-transmitted blue-stain fungus Ceratocystis polonica enhances tree resistance to later mass attack by this bark beetle. 2 Twenty-five mature trees were pretreated by inoculating a non-lethal dose of the fungus into the bark, while 18 trees served as untreated controls. Three and a half weeks after treatment a bark beetle attack was initiated by attaching dispensers with I. typographus pheromone to the tree trunks. 3 A significantly larger proportion (67%) of the control trees than of the pretreated trees (36%) were killed by the beetle attack. The result is discussed in relation to recent results regarding defence mechanisms in Norway spruce trees.     

Induced terpene accumulation in Norway spruce inhibits bark beetle colonization in a dose-dependent manner

Background

Tree-killing bark beetles (Coleoptera, Scolytinae) are among the most economically and ecologically important forest pests in the northern hemisphere. Induction of terpenoid-based oleoresin has long been considered important in conifer defense against bark beetles, but it has been difficult to demonstrate a direct correlation between terpene levels and resistance to bark beetle colonization.

Methods

To test for inhibitory effects of induced terpenes on colonization by the spruce bark beetle Ips typographus (L.) we inoculated 20 mature Norway spruce Picea abies (L.) Karsten trees with a virulent fungus associated with the beetle, Ceratocystis polonica (Siem.) C. Moreau, and investigated induced terpene levels and beetle colonization in the bark.

Results

Fungal inoculation induced very strong and highly variable terpene accumulation 35 days after inoculation. Trees with high induced terpene levels (n = 7) had only 4.9% as many beetle attacks (5.1 vs. 103.5 attacks m⁻²) and 2.6% as much gallery length (0.029 m m⁻² vs. 1.11 m m⁻²) as trees with low terpene levels (n = 6). There was a highly significant rank correlation between terpene levels at day 35 and beetle colonization in individual trees. The relationship between induced terpene levels and beetle colonization was not linear but thresholded: above a low threshold concentration of ∼100 mg terpene g⁻¹ dry phloem trees suffered only moderate beetle colonization, and above a high threshold of ∼200 mg terpene g⁻¹ dry phloem trees were virtually unattacked.

Conclusion/Significance

This is the first study demonstrating a dose-dependent relationship between induced terpenes and tree resistance to bark beetle colonization under field conditions, indicating that terpene induction may be instrumental in tree resistance. This knowledge could be useful for developing management strategies that decrease the impact of tree-killing bark beetles.     

Flight initiation and survival in the bark beetle Ips typographus (Coleoptera: Scolytidae) during the spring dispersal

Temperatures in the forest litter of Norway spruce Picea abies were recorded throughout the day to obtain environmental parameters that could be used to design realistic flight-activity experiments in the laboratory. Flight activity and survival were monitored electronically in plastic chambers where the conditions were controlled by an environmental chamber. Flight attempts of the bark beetle Ips typographus were initially lower in chambers with forest duff but were prolonged compared with those of beetles in chambers with a metal screen substrate. Small bark slabs and spruce twigs in the duff were utilized as food and extended the period of flight and survival. A thermal gradient in duff from 25° at the surface down to 13.8°C at a depth of 4 cm also slightly increased the survival of beetles compared with a constant 25°. A daily ambient temperature cycle as well as the duff thermal gradient increased the survival from about 3 d to more than 8 d. The latter length in the laboratory agreed with survival rates of caged beetles in a clearcut forest area, while beetles caged in the forest survival for more than 14 d. Temperatures were monitored at the duff surface of the caged beetles and compared with the catches of beetles that were attracted to a pheromone trap and collected with an electronic fraction collector. Information on flight and survival during the dispersal period is necessary to the design of ecologically sound management programs for control of bark beetles.     

Semiochemicals and bark beetle populations: Exploitation of natural phenomena by pest management strategists

An analysis of semiochemical communication between host trees, bark beetles and commensal or entomophagous insects discloses five principal means by which semiochemicals can influence the population dynamics of bark beetles. These are: mediation of aggregation and mass attack on new hosts, cessation of aggregation and shifting of attack to uninhabited hosts, induction of aggregation by competing species, inhibition of aggregation by competing species, and mediation of host finding by commensal and entomophagous insects. Further analysis suggests major points of natural vulnerability which lead to six fundamental strategies for potential pest management: prevention of production of aggregation pheromones, sabotage of olfactory perception, exploitation of semiochemical-based secondary attraction, exploitation of antiaggregation pheromones, exploitation of repellent allomones, and exploitation of the kairomonal response by entomophagous insects. Investigations of the many possible tactics arising from these strategies have led to three types of operational pest management programs: prevention of pheromone production by excluding bark beetles from their hosts; suppression of bark beetle populations through the utilization of semiochemical-baited traps, trees or logs; and the use of antiaggregation pheromones to protect vulnerable hosts from attack.     

Attraction of ambrosia and bark beetles to coast live oaks infected by Phytophthora ramorum

1 Sudden oak death is caused by the apparently introduced oomycete, Phytophthora ramorum. We investigated the role of bark and ambrosia beetles in disease progression in coast live oaks Quercus agrifolia. 2 In two Marin County, California sites, 80 trees were inoculated in July 2002 with P. ramorum and 40 were wounded without inoculation. Half of the trees in each group were sprayed with the insecticide permethrin [cyclopropanecarboxylic acid, 3‐(2,2‐dichloroethenyl)‐2,2‐dimethyl‐(3‐phenoxyphenyl) methyl ester] to prevent ambrosia and bark beetle attacks, and then were sprayed twice per year thereafter. After each treatment, sticky traps were placed on only the permethrin‐treated trees. Beetles were collected periodically in 2003. 3 Inoculated trees accounted for 95% of all beetles trapped. The ambrosia beetles Monarthrum scutellare and Xyleborinus saxeseni and the western oak bark beetle Pseudopityophthorus pubipennis were the most abundant of the seven species trapped. 4 Permethrin treatment delayed initiation of beetle attacks and significantly reduced the mean number of attacks per tree. Beetles did not attack any wounded or noncankered inoculated trees. 5 Trees with larger cankers trapped more beetles early in the disease. Once permethrin lost effectiveness, the number of beetle entrance tunnels was a more reliable predictor of subsequent trap catch than was canker size. 6 Beetles were initially attracted to P. ramorum cankers in response to kairomones generated in the host‐pathogen interaction. After beetles attacked the permethrin‐treated trees, aggregation pheromones most probably were the principal factor in beetle colonization behaviour.     

云杉八齿小蠹生态学研究进展

云杉八齿小蠹是欧洲最具危害性的小蠹虫之一,嗜食衰弱木,利用雄性产生的信息素进行大面积聚集。聚集信息素不仅具有引诱聚集的作用,其种类和数量还具有调节其聚集密度的效应。在定殖过程中,云杉八齿小蠹既能利用寄主挥发物定位寄主,也能利用非寄主挥发物作为远距离的嗅觉示踪来区别寄主和非寄主。在森林生态系统内捕食性天敌和寄生性天敌很大程度上影响着云杉八齿小蠹的种群密度和行为生态。本文从云杉八齿小蠹的分布与扩散、天敌的种类及控制作用、化学信息物质对小蠹虫及其天敌的行为调控作用以及信息素防治现状等方面进行了综述,并展望了其研究前景。